One method for forming hidden seam lines in covers for safety air bag assemblies include molding a shaped seam in a skin or cover molded from thermoplastic materials such as copolyether ester elastomers; polycarbonates; polyolefins; thermoplastic polyolefin alloys; polyurethanes; polyamides; polyacetals; thermoplastic polyester elastomers; polybutyleneterephthalate; polyethyleneterephthalate; acrylonitrile/butylene/styrene polymers and polystyrene. Examples of such molding processes are set forth in U.S. Pat. Nos. 4,246,213 and 4,895,389 issued respectively on Jan. 20, 1981 and Jan. 23, 1990 to Takmatsu et al and to Wesley D. Pack, Jr.
Another method for forming hidden tear seam lines in such covers is to use a knife to cut a groove in the inside surface of the cover to a depth the will produce a weakened section that will assure that the cover will separate upon deployment of the air bag against the inner surface of a door assembly that underlies the hidden tear seam in the cover as set forth in U.S. Pat. No. 5,082,310 issued Jan. 21, 1992 to Bauer.
While suitable for their intended purpose such methods are not useful in processes in which the cover is formed by casting an excess charge of thermoplastic resin on a heated thin metal shell mold to form a fused layer of the resin on the surface following which the excess amount of material is dumped from the heated thin metal shell mold leaving only the fused layer in place thereon. Examples of such processes are set forth in U.S. Pat. Nos. 4,217,325 and 4,664,864 both of which are owned by the assignee of the present invention and both of which are incorporated by reference.
The '325 and '864 patents do not disclose a process in which the deposited layer of material is imprinted in of the molded material while it is still plastic after all the excess material is dumped from the heated mold and while the mold is still open to expose the deposited layer of curing thermoplastic material.